This invention relates to a method for reducing the loss in the fertility of semen upon storage and to a collection kit for collecting semen which protects the semen from the effects of handling and thermal shock.
Although the total number of sperm in an ejaculate is a measure of the fertility thereof, a more important criteria is the percentage of sperm thereof which are motile.
Sperm is conventionally catagorized according to the motility thereof on a scale of 0 - 4 as shown below.
______________________________________ Degree of Motility Type of Motility ______________________________________ 0.degree. = No motility -- at most only tail movements without forward progression. 1.degree. = 20% or less showing progression (generally sluggish swimming movements). 2.degree. = 20 to 50% showing progression (generally good progressive swimming movements). 3.degree. = 50 to 80% showing progression (usually rapid swimming movements). 4.degree. = 80% and higher showing progression (usually very rapid swimming movements). ______________________________________
A plus (+) following the number means the percentage is nearer the upper than the lower limit of the percentage range.
The proportion of motile sperm showing progressive swimming movements is a measure of the fertility of the sperm sample, i.e., the likelihood that the sample will achieve fertilization. Marginally fertile semen contains an abnormally low percentage of sperm exhibiting progressive swimming movements and generally is rated 0.degree. or 1.degree. in the above scale.
Thus, although total sperm count is one criteria of the fertility of a sperm sample, a more important indicia of its fertility is the proportion of the sperm which exhibits progressive swimming movements. The proportion of progressively motile sperm is important because not only is it an indication of the amount of fertile sperm in the sample, it is also a measure of the quality of the sperm, i.e., a sperm sample of high quality is more likely to achieve fertilization than a sperm sample of poor quality containing the same total number of motile sperm because the high proportion of dead sperm and their decomposition products in the latter appear to inhibit fertilization.
In my prior application Ser. No. 531,728, filed Dec. 11, 1974, whose disclosure is incorporated by reference, there is disclosed a method for separating motile sperm from immotile sperm by maintaining at least the sperm portion of progressively motile sperm-containing semen, either as such or preferably as a suspension in an aqueous vehicle physiologically acceptable to the sperm, as an upper layer in vertical interfacial contact with a discrete lower layer of an aqueous contacting medium physiologically acceptable to the sperm in which the motile sperm has a lower migration rate than in the upper layer, until motile sperm of the semen have migrated into the contacting medium, thereby producing a contacting medium containing a sperm fraction having a higher proportion of motile sperm with enhanced Y-sperm content. Repeating the process with the thus-obtained sperm fraction and a second contacting medium in which the motile sperm have a still lower migration rate than in the first contacting medium, produces a sperm fraction consisting predominantly of motile Y-sperms.
Motile sperm is separated from immotile sperm in the first fractionation, thereby providing a highly motile sperm fraction of enhanced content of motile Y-sperm and normal morphology, thereby greatly enhancing the quality of the sperm.
In the process of my prior applications, the quality of the sperm is improved to such an extent that the motile-sperm-containing fraction can be introduced directly into the human uterus, thus further increasing the likelihood of a successful insemination. This is also important in artificial insemination of animals, e.g., mares and cows, where today diluted stored semen is introduced directly in the uterus. Although the incidence of unsuccessful inseminations is relatively low, a significant number of inseminations are unsuccessful and require repeat insemination, resulting in economic loss to the owner of the animal due to the delay in pregnancy and to the inseminator who must repeat the insemination. It is believed these unsuccessful inseminations are at least partially due to the introduction into the uterus of animals stored semen containing a high proportion of immotile, defective and dead sperm and their decomposition products. The separation process of that application reduces insemination failures resulting from the introduction into the animal's uterus of such undesirable components of semen.
However, total motile sperm count is also a relevant factor in determining sperm quality as well as the proportion thereof which have progressive movements. In animal inseminations, where the dilutability of semen is an important economic factor, and in marginally fertile human semen, where the total sperm count is often far below normal values, the total number of live sperm remaining after processing is an important factor in determining the likelihood of a successful insemination, i.e., residual total live sperm count as well as the quality of the sperm must be considered in any method involving handling and storage of the sperm. Therefore, the total number of motile sperm with progressive movements which survive storage is an important factor as well as the quality of sperm, i.e., the proportion of such sperm remaining after processing.
It is well known that, especially with human sperm, a substantial portion of the motile sperm originally present in a sample of semen become immotile and/or die upon freezing. See, e.g., Smith, K. D. and Steinberger, E., "Survival of Spermatozoa in a Human Sperm Bank: Effects of Long-term Storage," J.A.M.A. 223:774, 1973; Steinberger, E. and Smith, K. D., "Artificial Insemination with Fresh or Frozen Semen: A Comparative Study," J.A.M.A. 223:778, 1973. These losses are usually less with domestic animals and are tolerated because it is usually impractical or impossible to use collected semen fast enough to store it in an unfrozen state. Because of such large losses of motile sperm on freezing, the freezing of a plurality of samples of marginally fertile human semen and pooling them in order to obtain a high enough total motile sperm count to increase the chances of insemination was not feasible because even though the total motile sperm count of the pooled sample might be brought up to normal ranges, the ratio of motile sperm to immotile sperm therein would be unacceptable, i.e., the quality of the sperm would be too low for insemination purposes.
It is also known that handling of semen in an unfrozen state and subjecting it to rapid temperature changes reduces the motile sperm count thereof. With donors having normal motile sperm counts, such losses are not serious. However, when attempting to achieve pregnancy by artificial insemination, using the semen of the marginally fertile husband, such losses due to handling and/or temperature shock are intolerable and usually precludes the use of the husband's semen for artificial insemination purposes.
It is an object of this invention to provide a process for storing sperm in a frozen state which reduces the loss of motile sperm resulting from storage.
It is another object to provide a collection container for semen which reduces motile sperm losses in unstored semen due to handling and/or thermal shock.
Other objects will be apparent to those skilled in the art.